1. Technical Field
This invention relates to a production facility and a production method for small particles of metal being referred to by the name nano-particles. In general, nano-particles are particles having a size on a scale of less than one thousand nanometres, more preferably less than one hundred nanometres, in at least two spatial dimensions. The facility in accordance with the present invention is particularly versatile and it can be used for the production of various nano-particle morphologies. Therefore this facility is a cost efficient means for the production of industrially required nano-particle quantities and qualities.
There are many different technologies to produce nano-scale metal particles. Among others, it is known to employ a flow-through reactor. The energy for the production of nano-scale particles has to be offered to the production process.
2. Background Art
The flow reaction process for the production of nano-scale amorphous magnetic metals described in U.S. Pat. No. 5,766,306 A (inventor: Olli et al.; assignor: The Boeing Company; filing date: Jun. 4, 1996) uses sonochemistry for the decomposition of iron carbonyl and production of nano-particles with energy and environmental conditions of collapsing bubbles. Neat iron carbonyl is injected in a reactor and after sonic treatment a surfactant is added to keep particles separate in the magnetic separation process. Microwave energy is used to melt the particles and form larger particles from aggregates.
In the article by S. H. Huh et al. Rev. Sci. Inst. 70, Nr. 11, 4366 to 4369 (1999) an electrically heated filament is used to decompose metal carbonyls and nanometre sized metal particles are collected from an experimental setup closed reactor with one gas feeder (S. H. Huh et al. FIG. 1). The article also describes formation of alloy nanometre sized particles from iron and molybdenum.
It is known from the description of FIG. 6 of U.S. Pat. No. 6,716,525 B1 (inventor: Yadav et. al.; filing date: Jun. 18, 2003) that the residence time of an in-situ formed metal fine powder can be engineered by selecting the feed location.
A different approach is taught by U.S. Pat. No. 2,900,245 A (assignor: General Aniline & Film Corp.; filing date: Jan. 24, 1957). Like it is shown in the figure of said patent, in a closed loop process with an inert gas thermally decomposition of a metal carbonyl may be controlled by controlling conditions of temperature, pressure and gas velocity. Metal particles in a dimension of 1 micron size and bigger can be produced in said closed loop process by starting off from respective metal carbonyls. Additional information how a carbonyl decomposition process may be controlled by a vessel of which its free internal space is used as decomposition zone can be found in U.S. Pat. No. 1,836,732 A (assignor: I. G. Farbenindustrie A. G.; filing date: Mar. 4, 1930).
U.S. Pat. No. 5,064,464 (inventor: Y. Sawada et al.; assignor: Mitsubishi Chemical Company Ltd.; filing date: Nov. 9, 1989) claims production of ultrafine metal particles in a reactor with a process where a high temperature diluent gas from a conduit is brought in contact with a mixed gas with the transition metal carbonyl compound from a nozzle outlet of a conduit. Heat of 300 to 800° C. for decomposition is instantaneously supplied from high temperature diluent gas. Clogging of this conduit and nozzle outlet is prevented with a low temperature diluents gas from another conduit around the nozzle in a concentric configuration. All gases are mixed at the position of the nozzle. The reaction time for gas phase pyrolysis in the reaction tube is less than 5 seconds. A magnetic field is applied to nozzle outlet and reaction system. The nano-particles are recovered from a collection chamber.
The process disclosed in RU 2161549 C1 (inventor: A. G. Rjabko et al.; assignor: OAO INST GIPRONIKEL, OAO KOL SKAJA GORNO-METALLURGICHESKAJA KOMPANIJA; filing date: Jul. 4, 2000) is preferably used for the production of Ni-nanoparticles with controlled size in the range 0.5 μm to 5 μm, where control is obtained mainly by means of temperature. This method uses thermal decomposition of Ni carbonyl diluted with the diluent gas carbon oxide from 10 up to 80 vol. % with addition of oxygen by 0.01 to 0.1 vol. %. Ni carbonyl and the diluent gas are fed with two separate feeders into the reactor. The flow rates of Ni carbonyl are larger than 83 1/min, while the flow rates of carbon oxide, pre-heated to temperatures between 20 and 220° C. is larger than 333 1/min. The internal temperature of the decomposer is between 240 and 280° C., by means of the decomposer inner walls heated to a temperature up to 470° C.
The apparatus used in U.S. Pat. No. 3,955,962 (inventor: W. Dawihl et al.; assignor: Klockner-Werke A G; filing date: Apr. 14, 1975) for the production of metal fibers by agglomeration of metal atoms under the influence of flux lines in a direction normal to a supporting surface and opposite to a flow direction of metal carbonyls shows a plurality of three or four conduits and vaporizing devices connected to a chamber of the apparatus, so that a mixture of different vapours can be decomposed together.
Another approach using a microwave plasma apparatus and chemical synthesis technique leading to ultrafine powders is described in U.S. Pat. No. 6,409,851 B1 (inventor: S. M. Krupashankara et al.; assignor: Materials Modification Inc.; filing date: Mar. 5, 1999). After chemical reactions are carried out in the plasma gas of different constituents within a plasmatron, the ultrafine powders are formed by rapid quenching of reaction products in a reactor column. The plasmatron can have radial or axial injector ports as well as a feed port for a raw material dosing device for chemical interaction in the plasmatron. The powders formed from starting powders or vapours are then instantaneously quenched in a reaction column, leading to the ultrafine powders. Reactants and products can melt evaporate and recondense in the reaction column in order to form special sizes. Also metal carbonyls can be fed into a reactor column by means of a vaporiser for liquids, which is heated with water pipes, in order to quench ultrafine powders.
Even continuous high power CO2 lasers can be employed for pyrolysis of nickel carbonyls for the production of an aerosol of particles, which is described in US 2006/225 534 A1 (inventor: M. T. Swihart et al.; assignor The Research Foundation of State University of New York; filing date: Oct. 12, 2005). Sulfur hexafluoride is added to the precursor stream of gas as a photosensitizer because of poor IR absorption of nickel carbonyl. A distance between the laser beam and an inlet nozzle for gas can be adjusted. A flow of helium is entered into the reactor through tubing as a sheath gas confining the reaction zone to a small region near the axis of the reactor.
WO 2007/136 389 A2 (applicant: Directa Plus Patent & Technology Limited; priority date: Aug. 10, 2005) proposes to employ a flow-reactor vessel which may be operated in a certain temperature range, pressure range and with controlled amount of added energy. Thus, the process of producing nano-scale metallic particles is basically controlled by the environmental conditions within the reactor. In a further embodiment, the reactants can be borne on a stream like a fluid stream, especially an inert gas stream which may pass through an injector into the reactor vessel. While WO 2007/136 389 A2 proposes to operate the reactor by feeding at least one metal carbonyl, a similar patent application by the publication number WO 2007/021 768 A2 (applicant: Directa Plus Patent & Technology Limited; priority date: Aug. 10, 2005) refers to continuously feeding at least one decomposable moiety selected from a group of complexes or compounds.
Additional further details how to produce nano-scale particles may be derived from WO 2007/021 769 A2 (applicant: Directa Plus Patent & Technology Limited; priority date: Aug. 10, 2005), WO 2007/021 770 A2 (applicant: Directa Plus Patent & Technology Limited; priority date: Aug. 10, 2005), WO 2007/142 662 A2 (applicant: Directa Plus Patent & Technology Limited; priority date: Aug. 10, 2005).
All cited prior art documents are incorporated by reference which means that the scope of the cited documents may be considered to be incorporated by their subject matter in place of citing their publication numbers. This is done with the objective to avoid redefining generally known terms of the present invention newly although known by person-skilled-in-the-art.
While first tests and developments have shown that reactor-vessels in accordance to the before cited five patent applications WO 2007/021 768 A2, WO 2007/021 769 A2, WO 2007/021 770 A2, WO 2007/142 662 A2, WO 2007/136 389 A2 may have advantages for fast results different reactor designs may be advantageous for producing nano-scale particles in laboratory environments, in small quantities, or in a range of equal grades.